Kepler-22b is the first confirmed planet in the “habitable zone,” the area around a star where a planet could exist with liquid water on its surface, that has been discovered by NASA’s Kepler mission.

The planet’s radius is about 2.4 times that of the Earth. It is located about 600 light years away. Its orbital period is shorter than that of the Earth: a "year" on Kepler-22b is 290 days instead of 365.

Kepler-22b is 15% closer to its star and we are to the Sun. But since Kepler-22b's star is dimmer, lower in temperature and smaller than our Sun, researchers' modeling suggests it is a similar temperature to the Earth, said Bill Borucki, Kepler principal investigator at NASA's Ames Research Center.

"If the greenhouse warming were similar on this planet and had a surface, its surface temperature would be something like 72 Fahrenheit, a very pleasant temperature here on Earth."

The Kepler mission reported in February that it had found 54 planet candidates in the habitable zone; Kepler-22b is the first of these to be confirmed, and those results will be published in The Astrophysical Journal. There are still 48 potential planets from that batch.

Is life restricted to Earth, or could it exist somewhere like Kepler 22-b? It may be that the characteristics of Earth, with its particular position in the solar system, particular magnetic field strength and presence of larger planets like Jupiter make Earth very rare in having life (this is called the "Rare Earth Hypothesis.") But it's also possible that life in the universe is common, and we're only one example.